Anion exchange polymers and anion exchange membranes incorporating same

ABSTRACT

An anion exchange membrane is made by mixing 2 trifluoroMethyl Ketone [nominal] (1.12 g, 4.53 mmol), 1 Biphenyl (0.70 g, 4.53 mmol), methylene chloride (3.0 mL), trifluoromethanesulfonic acid (TFSA) (3.0 mL) to produce a pre-polymer. The pre-polymer is then functionalized to produce an anion exchange polymer. The pre-polymer may be functionalized with trimethylamine in solution with water. The pre-polymer may be imbibed into a porous scaffold material, such as expanded polytetrafluoroethylene to produce a composite anion exchange membrane.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patentapplication no. 62/303,294, filed on Mar. 3, 2016 and entitled AnionExchange Polymers and Anion Exchange Membranes Incorporating Same, theentirety of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is directed to unique anion exchange polymers and anionexchange membranes incorporating these polymers.

Background

Alkaline exchange membranes or anion exchange membranes (AEMs) allow forthe transportation of anions (e.g., OH⁻, Cl⁻, Br⁻) from the cathode tothe anode in an electrochemical reaction. Anion exchange membranes are acritical component of anion exchange membrane fuel cells, where hydrogenand oxygen are used to generate electricity, with water as a byproduct.anion exchange membranes are also used in water electrolysis, wherewater is split into hydrogen and oxygen using electricity. In both anionexchange membrane fuel cells and water electrolysis, hydroxide ions (OH)are transported through the anion exchange membrane, along with watermolecules. AEMs may also be used, for example, in batteries, sensors,electrochemical compressors, and as actuators.

Known anion exchange membranes are generally unsuitable for use in anionexchange membrane fuel cells or water electrolysis. Manycommercially—available anion exchange membranes are based onpolystyrene, which is generally considered a poor choice for anionexchange membranes fuel cells or water electrolysis. Other anionexchange membrane materials contain an arylene ether linkage (˜0˜) inthe mid-chain and a benzyltrimethyl ammonium group in the side-chain.This combination, however, has been found to be chemically unstable andto degrade easily under highly alkaline conditions.

Advanced alkaline membranes are also designed to have high ion exchangecapacity, which in turn means that they will have a tendency to swellwith absorption of water or a polar species. This swelling results inloss of strength and renders them less suitable mechanically forservice. In addition, this loss of mechanical properties implies a needfor thick membranes that in turn provides for higher ionic resistance.

There is therefore a need for a chemically stable Anion exchangemembrane with high ion exchange capacity, but also good mechanicalproperties that can be produced in thin films with low ionic resistance.

SUMMARY OF THE INVENTION

The invention is directed to anion exchange polymers and anion exchangemembranes incorporating these polymers and electrochemical systems suchas fuel cells or electrochemical pumps incorporating these anionexchange membranes.

In an exemplary embodiment, an anion exchange membrane comprises amixture of: 2 trifiuoroMethyl Ketone; 1 BiPhenyl; methylene chloride;and trifluoromethanesulfonic acid. These components may be mixed for amixing time and temperature to produce a pre-polymer and then thispre-polymer may be functionalized to produce an anion exchange polymer.The pre-polymer may be dissolved in methanol to produce a polymersolution. The pre-polymer may be functionalized by mixing withtrimethylamine in a solution comprising water, and/or methanol andsubsequently and drying the polymer solution. Functionalizing thepolymer while in the polymer solution state may increase thefunctionalization and thereby increase the conductivity of thesubsequent anion exchange polymer produced.

An exemplary anion exchange membrane may be produced by combining thepre-polymer with a scaffold material and subsequently functionalizingthe pre-polymer to produce a composite anion-exchange membrane. Thepre-polymer may be dissolved to produce a polymer solution as describedherein and this polymer solution may be imbibed into the porous scaffoldand subsequently dried to produce a composite anion exchange membrane. Afunctionalizing agent, such as trimethylamine may be combined with thepolymer solution before being imbibed into the porous scaffold or afterbeing imbibed in the porous scaffold. The scaffold may be a porousmembrane and may be a fluoropolymer membrane, such as expandedpolytetrafluoroethylene. A fluoropolymer membrane may be a preferredporous scaffold as it is non-reactive and can withstand high continuoustemperatures, such as 250° C. or more. A porous scaffold has porositythrough the thickness of the material to allow the anion exchangepolymer to extend and be connected from one side to a second andopposing side. A porous scaffold may be a planar material havingsubstantially planar sides and a thickness therebetween. The thicknessof a porous scaffold and a composite anion exchange membrane, may be nomore than about 100 μm, no more than about 50 μm, no more than 25 μm, nomore than about 15 μm and any range between and including the thicknessvalues provided. The thinner the composite anion exchange membrane, theless resistance there may be to anion transfer. A porous scaffold mayhave a high percentage of open area or pores, such as at least about50%, about 75% or more, about 85% or more, about 90% or more and even ashigh as 95% of more. The higher the concentration of the anion exchangepolymer, the more conductive the composite anion exchange membrane willbe.

The summary of the invention is provided as a general introduction tosome of the embodiments of the invention, and is not intended to belimiting. Additional example embodiments including variations andalternative configurations of the invention are provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention, andtogether with the description serve to explain the principles of theinvention.

FIG. 1 shows an exemplary polymer reaction of the present invention.

FIG. 2 shows an exemplary polymer of the present invention.

FIG. 3 shows an exemplary polymer reaction of the present invention.

FIG. 4 shows an exemplary polymer reaction to functionalize a polymer ofthe present invention.

FIG. 5 shows an exemplary porous scaffold having a first side anopposing second side and pores.

FIGS. 6 and 7 show a cross-sectional diagram of a composite anionexchange membrane comprising a porous scaffold, a pre-polymer that hasfunctional groups thereon.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Corresponding reference characters indicate corresponding partsthroughout the several views of the figures. The figures represent anillustration of some of the embodiments of the present invention and arenot to be construed as limiting the scope of the invention in anymanner. Further, the figures are not necessarily to scale, some featuresmay be exaggerated to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the presentinvention.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of elements is notnecessarily limited to only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus. Also, use of “a” or “an” are employed to describeelements and components described herein. This is done merely forconvenience and to give a general sense of the scope of the invention.This description should be read to include one or at least one and thesingular also includes the plural unless it is obvious that it is meantotherwise.

Certain exemplary embodiments of the present invention are describedherein and are illustrated in the accompanying figures. The embodimentsdescribed are only for purposes of illustrating the present inventionand should not be interpreted as limiting the scope of the invention.Other embodiments of the invention, and certain modifications,combinations and improvements of the described embodiments, will occurto those skilled in the art and all such alternate embodiments,combinations, modifications, improvements are within the scope of thepresent invention.

Referring now to FIG. 1 In one embodiment, the invention provides aionomer (7-Bromo-1,1,1-trifluoroheptan-2one (2)) was prepared accordingto literature or purchased commercially (ref: 647831-24-1 Molbase)

Accordingly, a mixture of 2 trifluoroMethyl Ketone [nominal] (1.12 g,4.53 mmol), 1 BiPhenyl (0.70 g, 4.53 mmol), methylene chloride (3.0 mL),trifluoromethanesulfonic acid (TFSA) (3.0 mL), and a magnetic stirringbar was stirred at room temperature under nitrogen. After ten hours, thereaction mixture solution became highly viscous and kept being stirredfor additional two hours. The resulting dark-brown, gel-like mass wasthen shredded with sonication and poured slowly into methanol. Whitefiber formed was filtered and washed with hot methanol. After dryingunder vacuum, 1.70 g of white fiber-like solid was obtained (97% yield).Or alternatively, a polymer according to the same general formula wherein each of R1 and R2 is, independently, a linear alkyl chain or a cyclicalkyl chain, and Z is selected from a group consisting of: a linearalkyl chain, a cyclic alkyl chain, and an alkylene ether chain.

The polymer is then dissolved in methanol (or one of generally wellknown organic solvents such as DMSO) at a 5% weight ratio i.e. 1 gram ofpolymer, 19 grams of methanol.

The mixture was then poured onto a 12 micron thick (Ref MBU200.012)expanded PTFE membrane supplied by TTG Inc. The mixture was then spreadusing a draw bar, and dried using a hot air dryer.

This process was repeated. The resulting membrane was 15 microns thick.The membrane was tear resistant, and folded comfortably withoutbreakage. It was therefore mechanically suitable for use, and thin.Those skilled in the art, can appreciate that this process can beperformed on a roll to roll, composite production system, with rollers,and draw bars in place; with hot air or other types of ovens in agenerally continuous process.

The membrane was then functionalized by dipping the membrane intrimethylamamine in solution with water to provide ion exchange capacitywith quaternized ammonium hydroxide.

Embodiments of the invention involve composites include a new class ofquaternized ammonium hydroxide-containing polymers prepared from astyrene-butadiene block copolymer (SEBS). This new class of polymers maybe used in alkaline exchange membranes (AEMs), lack an arylene etherlinkage in the polymer main-chain, and can prepared with any of a numberof quaternized ammonium groups in the polymer side-chains.

An SEBS, compound I, is employed where x and y are mol % of eachrepeating unit and 2x+y=100. For example, in some embodiments of theinvention, x is 15 and y is 70. Other values are possible, of course, aswill be recognized by one skilled in the art. An iridium-catalyzedborylation is then performed using bis(pinacolato)diboron (B2Pin2) tointroduce a boronic ester group into the aromatic rings of the SEBS,yielding compound II.

Polymers according to embodiments of the invention may be employed inany number of contexts, including, for example, as fuel cell alkalineexchange membranes, fuel cell ionomers, electrolysis alkaline exchangemembranes, as actuators, and in any number of battery applications, aswill be apparent to one skilled in the art.

One skilled in the art will also recognize, of course, that variouschanges, additions, or modifications of or to the methods describedabove may be made without substantively altering the compounds obtainedor their characteristics. Such changes, additions, and modifications aretherefore intended to be within the scope of the invention.

As shown in FIG. 5, an exemplary porous scaffold 10 has a thickness 30from a first side 20 an opposing 40 second side. The porous scaffold haspores 60 and an open structure that extends from the first to the secondside to allow a flow of fluid from a first to the second side. Theporous scaffold is permeable and will have a bulk flow of air from thefirst to the second side.

FIGS. 6 and 7 show a cross-sectional diagram of a composite anionexchange membrane 100 comprising a porous scaffold 10, a pre-polymer 80that has functional 90 groups thereon. As shown in FIG. 6, thepre-polymer forms a surface coating layer 120 on the first side 20 and asurface coating layer 140 on the second side of the porous scaffold. Asshown in FIG. 7, there is substantially no surface coating layer. Thefunctionalized pre-polymer is an anion exchange polymer 300.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any related or incorporated methods. Thepatentable scope of the invention is defined by the claims, and mayinclude other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.

It will be apparent to those skilled in the art that variousmodifications, combinations and variations can be made in the presentinvention without departing from the spirit or scope of the invention.Specific embodiments, features and elements described herein may bemodified, and/or combined in any suitable manner. Thus, it is intendedthat the present invention cover the modifications, combinations andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of making a composite anion exchangemembrane comprising the steps of: a) mixing the following components: i)2 trifluoromethyl ketone; ii) 1 biphenyl; iii) methylene chloride; andiv) trifluoromethanesulfonic acid, for a mixing time and temperature toproduce a pre-polymer, b) providing a porous scaffold; c) dissolving thepre-polymer in an imbibing solution comprising methanol to produce asolution of the pre-polymer; and d) combining the pre-polymer solutionand the porous scaffold by imbibing and subsequently functionalizing thepre-polymer; and e) drying the functionalized pre-polymer solution toproduce a composite anion exchange membrane.
 2. The method of making acomposite anion exchange membrane of claim 1, wherein the step offunctionalizing comprises exposing the pre-polymer to trimethylamine ina solution with water.
 3. The method of making a composite anionexchange membrane of claim 1, wherein the porous scaffold is an expandedpolytetrafluoroethylene membrane.